I went with this pattern. Any tips to laying this down? I was thinking an upside down U shape so that I could get the spacing down correctly. Finish the back (top) right, then work my way down to the bottom left.

Over ditra, I have Laticrete 4-xlt, and Bostik Ditra-set to choose from. I understand 4XLT is specifically rated for large tile, and seems to better but since it is modified, it will have to dry for much longer than Ditraset.

Ditraset on the other seems sufficient, and since not modified, does not have an extended dry time before grouting.

I'd want "much longer" defined. I used a lightly modified mortar, Prolite, to set my 12X24 porcelain floor tiles and less than a week later I had to pull one up. Well, I had to break one up to get it out. The mortar was definitely dry.

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Dan
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If I recall correctly my memory is excellent, but my ability to access it is intermittent.

Lenny, the DitraSet is suitable for use as a LHT mortar and it feels much like a modified mortar in use. Whichever of those mortars you have that is the most readily available and least expensive is the one I'd choose. The only advantage to the DitraSet would be that it is theoretically covered by a Schluter warranty, which you don't need.

I think I read from the ditra manual that you are "supposed" to let modified fully cure "much longer". Officially as much as 45-90 days, or something crazy like that, when sandwiched between tile and a non-breathing surface like ditra. I also read that nobody fully follows that recommendation, and many get away with it just fine, however they do follow some sort of extended waiting period before grouting.

Unmodified (ditra-set) has no such extended waiting time.

In the aftermath of my tile/supplies shopping fiasco, I have a bag of each currently sitting next to me. So if anyone has used either and was happy, or was particularly unhappy, that might help me choose. Or if it really doesn't matter, that is technically helpful

If it matters, I also plan to use spectralock grout to finish.

From my impressions, I want to use Ditra set since it appears to be easier (can mix partial bags, etc), 4XLT sounds like its better (at the expense of drying time), but I also have no experience.

Keep in mind that there is no tile industry standard at all. The TCNA Handbook has recently (I don't recall the year) added a note under Materials that the membrane must achieve a 50psi shear bond strength as measured by the method used for crack isolation membranes. That's also the same bond strength required for all waterproofing membranes. On a good day you can get that kind of strength out of a bottom-line dry-set (unmodified) mortar such as Custom's CustomBlend (maybe not every time, but sometimes). It's a very minimal requirement, but certainly an adequate one.

The Handbook recommends you follow the product manufacturer's recommendations, but that's a standard line that applies to building code as well. So, if you want to follow the Ditra manufacturer's recommendation, you'll use the DitraSet. If you think all other manufacturers of similar products have a better approach, you can use either mortar you have.

Sounds like "it doesn't matter". I'll go with Ditra-set. Since it is unmodified, am I safe mixing half batches? I have a scale so I can still measure accurately. Or are there still components of the thinset that can settle making small batches a bad idea?

I've used Ditra Set on a couple jobs several years ago and I've used modified thinset under and over Ditra on probably a hundred jobs, both without any problems. I feel that either thinset will lock into the Ditra waffles but my concern is the Ditra Set not bonding to the tiles as well. I try to give the floor an extra day to dry if possible but many times we have grouted the tiles the next morning. I'd use the modified.

You're over thinking the mixing. Pour a couple inches of water in a bucket and add thinset till it's about like pancake batter.

Regardless which thinet you use, force a skim coat into the backs of the tiles and comb the Ditra back and forth to make sure the waffles are full.

Well... too late, I used Ditraset. I did apply a generous backbutter, maybe between 1/8" and 1/4" thick, uniform, used 1/2x1/2 trowel on the floor, wiggled them, and beat them down with a rubber mallet. Pulled a few (VERY difficult to so while wet) and verified 100% full coverage. I am hoping I will be fine. I was too slow and only got the hard 2/3rds done... This was because the original plan was to thinset some Wedi-band at the drywall to ditra transition, but it wasn't going well, and was taking longer than I thought. After 30 minutes, I scrapped that idea.

I will now cut the drywall 1/4" above the finished tile (as necessary) to provide a gap so if there is a flood, walls might survive. Sound like a good plan?

Original plan was 2"x2" square mosaic for the floor, and larger at least 6"x18" maybe 12x24 for the shower walls.

After looking at the fake marble porcelain, it looks too "printed on" and I can't stand it. So I searched real marble... appearantly that is a bad idea. I think straight white feels too much like a hospital. So back to square one...

looking for something light/white but with a texture for the walls, and something a little darker and textured for the floor any terms/materials for what I am looking for that is low maintenance? Wish they made a fake marble that actually resembled real marble/granite, and not a bunch of printed dots splashed on the tile.

Finished the floor and grouted. Now I need some tips on some finishing details.

1) Drywall/wedi outside corner:
I just sealed the raw edge with Bullseye-123 primer. Then I plan to install plastic cornerbead, drywall mud on the drywall side, thinset on the wedi side. Feather out the drywall side with more mud, sand, paint, done. Then on the wedi side, I plan to use a rondec emedded in the thinset, under the tile (over the corner bead) to complete the corner and edge the tile at the same time. Anything I should do differently here?

2) Marble bathroom door threshold:
Bedroom side has hardwood floor (3/4" height from subfloor) plus tack strip (total ~1+1/8"). Carpet adds at least another 1/4" on top of the tack. I clearly need to make up at least 3/4" in depth, how do you recommend I do that? I have extra Ditra if that helps

Also, could use some input deciding whether to go single or double bevel. Single gives a lower profile overall, and would allow the option of a bare hardwood bedroom floor no carpet cleanly with no modifications. Double probably works/looks better if carpet is kept.

Looks good so far. Have you thought about going to your local granite/stone shop and see if you can find a remnant that matches your floor? I've seen a few varieties that would compliment the floor pretty well.

Ask them to cut and polish the top and front and back (long) sides in a eased or slightly beveled (like a marble threshold). If you find a remnant, they should charge you about $50-150 to make one custom fit. Average thickness is 1.125"-1.25". You can set it with flexbond or versabond.

Ali, I agree, remnant stone could really set things off with matching pieces for my shower curb and the niche shelves. Also, might save a bit by bundling all that together.

Dan, I was worried the edge might be too low relative to the carpet nap, good to know that is not the case. Do you think keeping the low side of the bevel flush with the top of the tack strip is a good idea? It should allow me the flexibility to choose carpet or hardwood for the bedroom floor in the future.

About installing the threshold, what should be done to fill the void? I have leftover lath, Ditra, and Advantech. But it seems that Advantech+Ditra would bring the threshold too high to sit on the hardwood floor. Would a medium bed thinset mortar like the 4XLT or ditraset on top of ditra work? They have a maximum thickness of 3/4" (which is the gap I need to fill) and the ditra should eat into that a bit for a good safety margin. If that is good to go, would I need to get a bigger trowel, or just carefully comb the top with my .5x.5" trowel?

The marble threshold I tore out had not a single crack, and was laid on a ~3/4" mortar bed with lath.

If eliminating the carpet is a future project I'd aim for that edge of the TH to be no higher than the tacking strip, especially since it's possible that the floors will need to be refinished. Depending on the thickness of the carpet backing you might find that the tacks poke through.

As Ali mentioned, a piece of solid stone matching the other bits you have (don't know why I didn't do that), is a great idea and it's likely to be 1 1/4" thick. Ditra will help isolate it from the subfloor, but I think pretty much anything will work, like a strip of ply. I used some scraps of foam board for mine. If you then use a thick layer of mortar to make up the rest of the height, mix it thick so there's less chance that the stone will sink (ask/don't ask me how I know).

If the length of the TH is tight you may find that you'll have to remove a piece of the jambs' door stop to get it in.

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Dan
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If I recall correctly my memory is excellent, but my ability to access it is intermittent.